Vacuum infiltrating of tungsten powder bodies with copper-titanium alloys



k A a 3 4 a i mm FIdZZ E. J. ZDANUK ETA!- VACUUM INFILTRATING 0FTUNGSTEN POWDER BODIES WITH COPPER-TITANIUM ALLOYS Filed March 11, 1966Feb. 7, 1967 FIGZQ INVENTORS CHARD H. KRO

WAR

I CK D J. ZDANUK ATTO RNEY United States Patent M 3,303,026 I VACUUMINFlLTRATlN-G 0F TUNGSTEN POW- DER BODES WITH COPPER-TIT 11 ALLOYSEdward J. Zdanuk, Lexington, and Richard H. Krock, Peabody, Mass.,assignors to l. R. Mallory & Co. Inc., Indianapolis, Ind, a corporationof Delaware Filed Mar. 11, 1966, Ser. No. 533,579 9 Claims. (Cl. 75-408)The present invention relates to powder metallurgy and more particularlyto improved means and methods of providing composite materials for useas an electrical contact material.

It was found that using vacuum infiltration techniques, acopper-titanium alloy, titanium sandwiched between copper and a tungstenpowder body subsequently heated to form a copper-titanium alloy, atungsten powder body coated with titanium by electrolytic or vapor phaseplating, and the like wet individual particles of the tungsten powderbody so as to allow infiltration of the powder body withcopper-titanium. The resultant composite body was found to have a highconcentration of titanium in the interface region between the tungstenparticles and the copper-titanium alloy thereby raising the overallelectrical conductivity of the copper-titanium alloy matrix. The use ofvacuum infiltration techniques also decreases the volume of hydrogenpresent in the resultant tungstencopper-titanium composite by more thanan order and decreases the volume of all gaseous components by severalorders.

Although complete and substantially instantaneous infiltration of copperinto sintered tungsten bodies is conveniently carried out in anatmosphere of hydrogen, a copper melt shows no penetration into tungstenpower bodies in a vacuum atmosphere using comparable timetemperaturetreatments and using standard metallurgical procedures. In carrying outthe present invention, it was found that subjecting the tungsten powderbody and a contacting copper-titanium alloy to a vacuum infiltrationprocess, the copper-titanium alloy was absorbed into the tungsten bodyby capillary attraction. It is thought that the titanium promoteswetting of the tungsten particles by the copper-titanium alloy.

Tungsten is used in electrical contact materials because of its inherentcharacteristics of hardness and of resistance to arcing which reducepitting of the tungsten contact material. However, pure tungsten contactmaterial possesses high electrical resistance which lowers theefficiency and reliability of the tungsten contact material.

It has been suggested that a composite of tungstencopper used as anelectrical contact material would make advantageous use of the severaloutstanding characteristics of both metals. In the composite, the copperprovides the current carrying capability and thermal conductivity whilethe tungsten contributes hardness, resistance to are erosion, andsuperior anti-weld properties. In order to utilize the aforementionedcharacteristics of the copper and the tungsten, it is necessary tofabricate the metal into a tungsten-copper composite.

Copper and tungsten are mutually insoluble and form no alloys in themetallurgical sense, but mixtures of the two metals are usually referredto as alloys but are, technically speaking, composites. Composites oftungstencopper may be prepared by pressing the mixed metal powders tothe required shape in dies, and subsequently sintering in a hydrogenatmosphere above the melting point temperature of the copper, preferablybetween l250 and l350 centigrade. The hydrogen acts as a flux and themolten copper wets the tungsten particles and cements them together.Another method which provides a harder resultant body consists of firstpressing and 3,303,026 Patented Feb. 7, 1967 sintering the tungstenpowder so as to form a coherent but porous body, which is then heated ata temperature of about 1200 C. to 1300 C. in a hydrogen atmosphere andin contact with molten copper. The copper is absorbed into the pores ofthe tungsten powder body by capillary attraction. The copper infiltrantimparts strength and ductility to the tungsten powder body and alsoprovides the resultant body with higher current carrying capability andthermal conductivity. However, using standard metallurgical procedures,a copper melt shows no penetration into the tungsten powder body in avacuum. It is thought that the lack of penetration of the copper intothe tungsten powder body is due to the unfavorable surface energies thatare present in the vacuum.

If there is no solubility between the metals as is the situation betweentungsten and copper, and if the wetting is poor, an auxiliary agent forinfluencing the surface energies in the desired direction is required.

It was found that by utilizing small amounts of titanium and by usingvacuum infiltration techniques a melt of copper-titanium completelyinfiltrated the tungsten powder body. It is thought the titanium eitherraises the surface energies of the melt or of the solid, or lowers thesurface energy of the interface between the melt and the solid therebyfavoring infiltration of the melt into the tungsten powder body. It isthought the vacuum serves the dual purpose of allowing penetration ofthe coppertitanium melt into the tungsten powder body and ofsignificantly decreasing the volume of all gases present. However, theresultant tungsten-copper-titanium contact material must contain a lowvolume of gas before the material is acceptable for application invacuum environments.

Therefore, it is an object of the present invention to provide acomposite material suitable for use as a contact material in vacuumelectrical switching devices.

Another object of the present invention is to provide a compositematerial of tungsten particles in a matrix of copper titanium for use asan electrical contact material wherein the concentration of titanium inthe tungsten interface region is much higher than the concentration oftitanium between the tungsten particles thereby raising the overallelectrical conductivity of the copper-titanium alloy matrix.

Yet another object of the present invention is to provide a means andmethod of vacuum infiltrating a refractory material with an electricallyconducting material thereby providing a composite contact material whichis low in gas content and low in material which may be converted to gasduring operation of the contact.

Yet still another object of the present invention is to provide meansand methods of using a copper-titanium alloy as infiltration stock fortungsten powder bodies so as to allow complete vacuum infiltration ofthe tungsten powder body thereby providing a composite contact materialhaving integrally joined tungsten-copper-titanium materials.

A further object of the present invention is to provide means andmethods of fabricating a composite contact material using vacuuminfiltration techniques, the composite contact material having highelectrical and thermal conductivity, combined with low erosion underarcing and low deformation under pressure environments.

Another object of the present invention is to provide an alloy whichincludes an agent that wets the tungsten, that is ductile, that has highelectrical and thermal conductivity, and includes a melting point thatis lower than tungsten.

The present invention, in another of its aspects relates to novelfeatures of the instrumentalities of the invention described herein forteaching the principal object of the invention and to the novelprinciples employed in the instrumentalities whether or not thesefeatures .and principles may be used in the said object and/ or in thesaid field.

With the aforementioned objects enumerated, other objects will beapparent to those persons possessing ordinary skill in the art. Otherobjects will appear in the following description and in the appendedclaims.

In the drawings:

FIGURE 1 is a photomicrograph of about 500 magnifications of atungsten-copper-titanium composite contact material showing a sinteredtungsten specimen completely vacuum infiltrated with a copper-titaniumalloy containing about 0.5 percent by weight, titanium. The infiltrationwas carried out at 1250 C. for 1 hour at a pressure of 10 torr.

FIGURE 2 is a photomicrograph of 500 magnifications of atungsten-copper-titanium composite contact material illustrating acompacted tungsten specimen completely vacuum infiltrated with acopper-titanium alloy containing about 0.5 percent, by weight, titanium.FIGURE 2 also shows a greater dispersion of the tungsten powders in thecopper-titanium matrix than is shown in FIGURE 1 using comparablesintering time-temperature.

FIGURE 3 is an enlarged cross-sectional view of atungsten-copper-titaniurn composite contact material showing a sinteredtungsten specimen that is about 90 percent vacuum infiltrated with acopper-titanium alloy containing about 0.2 percent, by weight, titaniumusing the temperature treatments used in FIGURES 1 and 2, but lesseningthe time of the temperature treatment to 30 minutes.

FIGURE 4 is an enlarged cross-sectional view of atungsten-copper-titanium composite contact material illustrating asintered tungsten specimen about 30 to 40 percent vacuum infiltratedwith a copper-titanium alloy containing about 0.05 percent, by weight,titanium using the temperature treatments used in FIGURES 1 and 2 butreducing the length of the temperature treatment to 20 minutes.

FIGURE 5 is an enlarged cross-sectional view of atungsten-copper-titanium composite contact material illustrating asintered tungsten specimen that was completely vacuum infiltrated by thecopper-titanium alloy containing about 0.05 percent, by weight, titaniumby subjecting the specimen to a temperature of 1450 C. for the timeduration of FIGURE 4.

Generally speaking, the means and methods of the present inventionrelate to an electrical contact material for use in a switching devicesuch as, for example, in a vacuum electrical power switching means. Thecontact material consists of a tungsten body completely vacuuminfiltrated by a copper-titanium alloy. The copper-titanium alloyconsists of 0.5 to 0.05 percent, by weight, titanium, the remaindercopper.

The method of making a tungsten body infiltrated with an alloy of coppercomprises the steps of compacting powdered tungsten particles into adesired body shape. The tungsten body is contacted with acopper-titanium alloy which when heated above its melting point makesuse of its ability as an agent for wetting the tungsten particles. Thetungsten body and the contacting copper alloy are placed in a vacuumatmosphere and heated so as to completely vacuum infiltrate the tungstenbody with the copper alloy by capillary attraction thereby forming acomposite contact material.

More particularly, the means and methods of the present invention relateto fabricating a tungsten body infiltrated with an alloy ofcopper-titanium for use as an electrical contact in vacuum environments.The tungsten powder has a particle size ranging between 1 and micronsand is compacted under pressure ranging from 20 to 35 tons per squareinch into a desired body shape. The tungsten body may be presintered ina hydrogen atmosphere at about 1250 centigrade for about 10 minutes.

The surfaces of the sintered tungsten body are contacted with an alloyof copper-titanium. The copper-titanium alloy consisted of 0.05 to 0.5percent, by weight, titanium, the remainder copper. The titanium is usedto promote the wetting of the tungsten particles by the copper-titaniumalloy. The tungsten body and the contacting copper-titanium alloy areplaced in a vacuum atmosphere having -a pressure of about 10' torr andheated at a temperature of between 1250 and 1450 centigrade for a timeduration of between 20 minutes and 60 minutes. The tungsten 'body iscompletely vacuum infiltrated with the copper-titanium alloy therebyforming a tungstencopper-titanium composite for use as a contactmaterial in vacuum environments.

In carrying out the present invention, it was found for atungsten-copper system, an alloy of copper-titanium having small amountsof titanium when brought into contact with the tungsten powder body in aheated vacuum environment resulted in the copper-titanium completelyinfiltrating the tungsten powder body and forming a dense compositematerial. It is thought that the small amount of titanium is sufficientto either raise the surface energies of the melt of copper-titanium orof the tungsten particles or lower the surface energy of the interfacebetween the melt and the solid.

The resultant composite is dense and ha high electrical and thermalconductivity combined with a high resistance to deformation underpressure.

In forming the tungsten powder body, a suitable mold is utilized to formthe tungsten powder into a desired shape. The size of the particles oftungsten may vary in accordance with the desired density of thecomposite contact material and with the desired pore size distributionof the composite contact material. For illustrative purposes, tungstenpowder having a particle size of about 1 micron to 10 microns isutilized. However, it should be understood that tungsten powder having alarger or a smaller particle size may be used.

The tungsten particles are compacted within the confines of a suitablemold by a compacting pressure ranging between 20 and 35 tons per squareinch thereby forming a porous tungsten body. If it is desired to furtherstrengthen the tungsten body prior to infiltration and/or provide acomposite having a higher tungsten content, the tungsten body may besintered in an atmosphere of hydrogen at a temperature of about 1250 C.for a time duration of about 10 minutes. FIGURE 1 shows a compositestructure wherein the tungsten compact was presintered. After thepreparatory treatment is completed, the strength of the tungsten compactis materially increased, and the compact can be handled readily. Verylittle grain growth takes place during the presinter treatment, and theincrease in strength of the compact may be due to the reduction of thesurface film of oxide on the individual tungsten particles, the reducedmetal acting as a cement which binds the tungsten particles together.

It should be pointed out that the presinter of the tungsten compact inthe hydrogen atmosphere is not a necessary prerequisite to thesuccessful infiltration of the tung sten powder body with thecopper-titanium alloy. FIG- URE 2 shows a tungsten powder body which wasnot presintered but is completely vacuum infiltrated with thecopper-titanium alloy.

The dispersion differential of the tungsten particles between FIGURE 1and FIGURE 2 should be noted. The dispersion of the tungsten particlesin FIGURE 2 is greater than the dispersion of the tungsten particles ofFIGURE 1 due only to the fact that the tungsten specimen of FIG- URE lwas subjected to a presintering step whereas the specimen of FIGURE 2was not.

The tungsten specimen, presintered or not, is placed in a vacuum havinga pressure of 10 torr or less and contacted with a copper-titanium alloycontaining about 0.5 percent, by weight, or less of titanium. Thetungsten specimen and the contacting copper-titanium alloy is heated toa temperature of between about 1200 C. to 145 C. The range oftemperatures exceeds the 1085 C. melting point temperature of thecopper-titanium alloy but is below the 3410 C. melting point temperatureof tungsten.

A chemical analysis of the resultant composite body showed that vacuumprocessing decreases the volume of hydrogen by more than an order anddecreases the volume of other gaseous components by several orders.

An electron probe analysis of the region between tungsten particlescomposed of the copper-titanium alloy showed a segregation or a highconcentration of titanium in the interface region between the tungstenand coppertitanium alloy. This would explain how relatively smalladditions of titanium can remain highly active during the extensivepenetration of the tungsten body by the infiltrant.

Due to the gradation in titanium concentration in the copper-titaniumalloy, which produces a much higher concentration of titanium in thetungsten interface region than the nominal concentration in theinfiltration stock, the bulk of the region between the tungstenparticles contains a much lower concentration of titanium than that usedin the infiltration stock. Since titanium in solid solution lowers theconductivity of copper, the titanium segragation has a dual advantage,that is, in addition to promoting the wetting and infiltration in avacuum environment, the segregation also raises the overall electricalconductivity of the infiltration alloy above that which would beexpected from the nominal concentration :of the infiltration stock.

Referring to the drawings, FIGURE 1 illustrates atungsten-copper-titanium composite 10 consisting of a sintered porouscomp-act of tungsten particles 11 which has been completely infiltratedby a coherent network of coppertitanium 12. The metal surfaces of thecopper-titanium mixture are integrally bonded with the tungstenparticles. The copper-titanium alloy used to contact the tungsten powderbody prior to vacuum infiltration contains about 0.5 percent, by weight,titanium. During vacuum infiltration, the porous tungsten body and thecontacting alloy were subjected to a temperature of about 1250 C. forabout 60 minutes at a pressure of 10 torr, or less.

FIGURE 2 shows a tungsten-copper-titanium composite 13 similar to thatof FIGURE 1 except that the initial tungsten compact was not sinteredprior to the vacuum infiltration.

The dispersion diiterential of the tungsten particles between FIGURE 1and FIGURE 2 should be noted. The dispersion of the tungsten particlesin FIGURE 2 is greater than the dispersion of the tungsten particles inFIGURE 1 due only to the fact that the tungsten specimen of FIG- URE 1was subjected to a presintering treatment.

FIGURE 3 illustrates a tungsten-copper-titanium composite 14 consistingof a sintered porous compact of tungsten particles about 90 percentinfiltrated by a coherent network of a copper-titanium mixture. The area25 represents void spaces among the tungsten particles, that is, an areanot infiltrated with copper-titanium. The metal surfaces of thecopper-titanium mixture are integrally bonded to the surfaces of thetungsten particles. The

copper-titanium alloy used to contact the porous tungsten body prior tovacuum infiltration contains about 0.2 percent, by weight, titanium.During vacuum infiltration, the porous tungsten body and the contactingalloy were subjected to a temperature of about 1250 C. for about 30minutes at a vacuum pressure of torr, or less.

FIGURE 4 shows a tungsten-copper-titanium composite 17 consisting of asintered porous compact of tungsten particles about 30 to 40 percentvacuum infiltrated by a coherent network of a copper-titanium alloy. Thearea 26 represents void spaces among the tungsten particles, that is, anarea not infiltrated with copper-titanium. The metal surfaces of thecopper-titanium mixture are integrally bonded with the surfaces of thetungsten particles. The copper-titanium alloy used to contact the poroustungsten body prior to vacuum infiltration contains about 0.05 percent,by weight, titanium. During vacuum infiltration, the porous tungstenbody and the contacting alloy were subjected to a temperature of about1250 C. for about 20 minutes at a vacuum pressure of 10" torr or less.

FIGURE 5 illustrates a tungsten-copper-titanium com posite 19 completelyvacuum infiltrated with the coppertitanium alloy. The alloy containedabout 0.05 percent, by weight, of titanium, like the alloy used toproduce the composite of FIGURE 4. The porous tungsten body and thecontacting alloy were subjected to a temperature of about 1450 C. forabout 20 minutes at a vacuum pressure of 10 torr or less.

The tungsten-copper-titanium composites illustrated in FIGURES 1 to 5illustrate that a decreasing amount of infiltration into the tungstenbody takes place with a decreasing amount of titanium present in thecopper-titanium alloy and/or a decreasing time-temperature treatment.FIGURE 5 shows that the reduced amount of titanium in thecopper-titanium alloy and/ or decreased heating time can be compensatedfor by increasing the heating temperature to which the tungsten body andthe contacting copper-titanium alloy are subjected.

The following Examples 1 to 5 are illustrative of the preparation of atungsten-copper-titanium contact material by vacuum infiltration of atungsten powder body with a copper-titanium alloy.

Example 1 A sintered tungsten body completely vacuum infiltrated by analloy of copper-titanium, the alloy containing about 0.5 percent, byweight, titanium, the remainder copper.

Powdered tungsten having a particle size of about 1 to 10 microns waspressed by any suitable means such as by an automatic press at about 20tons per square inch to provide a green compact sturdy enough to behandled. The green compact was presintered at about 1250 C. for about 10minutes in an atmosphere of hydrogen so as to form a skeleton typestructure. The presintering of the compact serves to increase thestrength of the compact 'by cementing the tungsten particles each to theother thereby binding them together. The sintered porous compact iscontacted with an alloy of coppertitanium having a titanium content ofabout 0.5 percent, by weight, the remainder copper. The sinteredtungsten compact and the contacting alloy of copper-titanium are placedin a vacuum atmosphere having a pressure of about 10 or less and areheated at a temperature of about 1250 C. for a time duration of about 1hour. The porous tungsten body was found to be completely vacuuminfiltrated by the copper-titanium mixture. The resultanttungsten-copper-titanium composite is illustrated in FIG- URE 1 of thedrawing.

Example 2 A green tungsten powder body completely vacuum infiltrated byan alloy of copper-titanium, the alloy of copper-titanium containingabout 0.5 percent, by weight, titanium, the remainder copper.

Powdered tungsten having a particle size of about 1 micron to about 10microns was pressed by any suitable means such as by an automatic pressat about 20 tons per square inch to provide a green compact sturdyenough to be handled. The porous green compact is contacted with analloy of copper-titanium having a titanium content of about 0.5 percent,by weight titanium, the remainder copper. The green tungsten compact andthe contacting alloy of copper-titanium are placed in a vacuumatmosphere having a pressure of 10* torr or less and are heated at about1250 centigrade for about 1 hour. The porous tungsten body was found tobe completely infiltrated by the copper-titanium alloy. The resultanttungsten-coppentitanium composite is illustrated in FIG- URE 2 of thedrawings.

The dispersion diiferential of the tungsten particles should be notedbetween the sintered tungsten specimen of FIGURE 1 and the green compacttungsten specimen and FIGURE 2. The dispersion of the tungsten particlesof FIGURE 2 is greater than the dispersion of the tungsten particles ofFIGURE 1.

Example 3 A sintered tungsten body about 90 percent vacuum infiltratedby an alloy of copper-titanium, the alloy of copper-titanium containingabout 0.2 percent, by weight, titanium, the remainder copper.

Powdered tungsten having a particle size of about 1 micron to about 10microns was pressed by any suitable means such as by an automatic pressat about 20 tons per square inch to provide a green compact sturdyenough to be handled. The green compact was sintered at a temperature ofabout 1250 centigrade for about 10 minutes in a hydrogen atmosphere. Thesintered porous tungsten compact is contacted with an alloy of about 0.2percent, by weight, titanium, the remainder copper. The sinteredtungsten compact and the contacting alloy of copper-titanium are placedin a vacuum atmosphere having a pressure of 10- torr or less and heatedat about 1250 centigrade for about 30 minutes. The porous tungsten bodywas found to be 90 percent infiltrated by the copper-titanium alloy. Theresultant tungsten-copper-titanium is illustrated in FIGURE 3 of thedrawings.

It should be noted that a decrease in the amount of titanium in thecopper-titanium alloy and/ or infiltration time results in porous areasremaining in the tungsten specimen. The pores can be closed byincreasing the infiltration temperature and/or the infiltration time.

Example 4 A sintered tungsten body about 30 to 40 percent vacuuminfiltrated by an alloy of copper-titanium, the alloy of copper-titaniumcontaining about 0.05 percent, by weight, titanium, the remaindercopper.

Powdered tungsten having a particle size of about 1 micron to aboutmicrons was pressed by any suitable means such as by an automatic pressat about 20 tons per square inch to provide a green compact sturdyenough to be handled. The green compact was sintered at about 1250centigrade for about 10 minutes in a hydrogen atmosphere. The sinteredporous tungsten compact was contacted with an alloy containing about0.05 percent, by weight, titanium, the remainder copper. The sin teredtungsten compact and the contacting alloy of copper-titanium were placedin a vacuum atmosphere having a pressure of 10* torr or'less and wereheated at about 1250" centigrade for about 20 minutes. The poroustungsten body was found to be 30 to 40 percent infiltrated by thecopper-titanium alloy. The resultant tungsten-copper-titanium compositeis illustrated in FIG- URE 4 of the drawings. The pores can be closed byincreasing the infiltration temperature and/or the infiltration time.

Example 5 A sintered tungsten body completely vacuum infiltrated by analloy of copper-titanium, the alloy of coppertitanium containing about0.05 percent, by weight, titanium, the remainder copper.

Powdered tungsten having a particle size of about 1 micron to about 10microns was pressed by any suitable means such as by an automatic pressat about 20 tons per square inch to provide a green compact sturdyenough to be handled. The green compact was sintered at a temperature ofabout 1250 centigrade for a time duration of about 10 minutes in ahydrogen atmosphere. The sintered porous tungsten compact was contactedwith an alloy of about 0.05 percent, by weight, titanium, the remaindercopper. The sintered tungsten compact and the contacting alloy ofcopper-titanium were placed in a vacuum atmosphere having a pressure of10- torr or less and were heated at about 1450 centigrade for about 8 20minutes so as to form a structure similar to FIGURE 2. The poroustungsten body was found to be completely vacuum infiltrated by thecopper-titanium alloy by increasing the infiltration temperature overthat recited in Example 4. The resultant tungsten-copper-titaniumcomposite is illustrated in FIGURE 5 of the drawings.

It is thought that the tungsten powder body or the presintered tungstenbody may be coated with titanium by electrolytic or vapor phase plating,impregnation of the coated body could be carried out successfully withessentially pure (unalloyed) copper. Vacuum impregnation will occur aslong as titanium is at the boundary. The amount of plated titanium wouldbe such that its composition would amount to 0.5 to 0.05 percent byweight of that of the amount of copper required to fill the voids.

The present invention is not intended to be limited to the disclosureherein, and changes and modifications may be made by those skilled inthe art without departing from the spirit and the scope of the presentinvention. Such modifications and variations are considered to be withinthe purview and the scope of the present invention and the appendedclaims.

Having thus described our invention, we claim:

1. A method of making a tungsten powder body infiltrated with an alloyof copper for use as an electrical contact material in vacuumenvironments comprising the steps of compacting tungsten particles intoa desired body shape; contacting the surfaces of the compacted tungstenbody with copper and titanium, said titanium for promoting the wettingof said tungsten particles; placing said tungsten body and saidcontacting copper and titanium in a vacuum atmosphere; and heating saidtungsten body and said contacting copper-and titanium so as tocompletely vacuum infiltrate said tungsten body with an al- 10y ofcopper-titanium thereby forming a composite material for use as acontact material in a vacuum switching device.

2. The method according to claim 1 wherein said tungsten body iscontacted with said titanium by electrolytic plating.

3. The method according to claim 1 wherein said tungsten body iscontacted with said titanium 'by vapor phase plating.

4. The method according to claim 1 wherein said copper alloy consists ofabout 0.5 to 0.05 percent, by weight, titanium, the remainder copper.

5. The method according to claim 1 wherein said vacuum atmosphere has apressure of not more than 10- torr.

6. The method according to claim 1 wherein said heating is to atemperature of between about 1250 C. and 1450 C. for a time duration ofbetween about 20 minutes and 60 minutes.

7. The method according to claim 1 wherein the particle size of saidtungsten is between about 1 to 10 microns.

8. The method according to claim 1 wherein the compacting pressure isabout 20 tons per square inch.

9. The method according to claim 1 including the ad ditional step ofsintering said compacted tungsten body in a hydrogen atmosphere at atemperature of about 1250 C. for a time duration of about 10 minutes.

References Cited by the Examiner UNITED STATES PATENTS 2,401,221 5/1946Bourne -208 2,456,779 12/1948 Goetzel 29182.1 2,612,443 9/1952 Goetzelet al. 75-200 2,797,300 6/1957 Hawthorne 75-164 2,870,485 1/1959 Jones75164 3,069,757 12/1962 Beggs et al. 29182.1

CARL D. QUARFORTH, Primary Examiner. R. L. GRUDZIECKI, AssistantExaminer.

1. A METHOD OF MAKING A TUNGSTEN POWDER BODY INFILTRATED WITH AN ALLOYOF COPPER FOR USE AS AN ELECTRICAL CONTACT MATERIAL IN VACUUMENVIRONMENTS COMPRISING THE STEPS OF COMPACTING TUNGSTEN PARTICLES INTOA DESIRED BODY SHAPE; CONTACTING THE SURFACES OF THE COMPACTED TUNGSTENBODY WITH COPPER AND TITANIUM, SAID TITANIUM FOR PROMOTING THE WETTINGOF SAID TUNGSTEN PARTICLES; PLACING SAID TUNGSTEN ODY AND SAIDCONTACTING COPPER AND TITANIUM IN A VACUUM ATMOSPHERE: AND HEATING SAIDTUNGSTEN BODY AND SAID CONTACTING COPPER AND TITANIUM SO AS TOCOMPLETELY VACUUM INFILTRATE SAID TUNGSTEN BODY WITH AN ALLOY OFCOPPER-TITANIUM THEREBY FORMING A COMPOSITE MATERIAL FOR USE AS ACONTACT MATERIAL IN A VACUUM SWITCHING DEVICE.